Method and apparatus for hot rolling

ABSTRACT

THE METHOD AND APPARATUS FOR HOT ROLLING STRIP BETWEEN A FINAL PAIR OF REDUCING ROLLS AND A PENULTIMATE PAIR OF REDUCING ROLLS IN WHICH THE FINAL ROLLS ARE DRIVEN AT A CONSTANT SPEED AND THE PENULTIMATE ROLLS ARE DRIVEN AT A VARIABLE SPEED LESS THAN THE CONSTANT SPEED. THE SPEED OF THE PENULTIMATE ROLLS IS INCREASED WHEN THE STRIP BETWEEN THE PENULTIMATE AND FINAL ROLLS IS IN A SUBSTANTIALLY STRAIGHT PASS AND DECREASED WHEN THE STRIP RISES TO A PREDETERMINED   DISTANCE ABOVE THE STRAIGHT PASS, THUS MAINTAINING THE STRIP BETWEEN THE ROLLS BETWEEN ZERO TENSION AND A SLIGHT COMPRESSION.

- a ,1 H. G. FROSTICKY 3,553,993

METHOD AND APPARATus FOR HOT ROLLING -Fi1e1..1an. -s1, 19 9 2 Sheds-Sheet 1 j/E I INVENTOI? HAROL D G. F ROS T [CK v Alto/nay .-I.am.1.2, 1971 H. G. FROSTICK 3,53,993

METHOD AND APPARATUS FOR HOT ROLLING Filed Jan. 31, 1969 2 ShetS-Sheet HAROLD G. F R05 7' [CK By 7;; Z

A rrornay United States Patent METHOD AND APPARATUS FOR HOT ROLLING Harold G. Frostick, North Palos Township, Cook County,

Ill., assignor to United States Steel Corporation, a

corporation of Delaware I Filed Jan. 31, 1969, Ser. No. 795,650

Int. Cl. B21b 37/00 US. Cl. 72-11 6 Claims ABSTRACT OF THE DISCLOSURE The method and apparatus for hot rolling strip between a final pair of reducing rolls and a penultimate pair of reducing rolls in which the final rolls are driven at a constant speed and the penultimate rolls are driven at a variable speed less than the constant speed. The speed of thepenultimate rolls is increased when the strip between the penultimate and final rolls is in a substantially straight passand decreased when the strip rises to a predetermined distance above the straight pass, thus maintaining the strip between the rolls between zero tension and a slight compression.

This invention relates to a method and apparatus for continuously rolling hot strip. For metallurgical reasons it is desirable to maintain a constant speed on the last stand of the roughing train of the mill. It is also desirable from the cost standpoint to position the last two stands as close together as possible. However, prior to my invention, it was not possible to combine these two features without necking down the width of the strip between the stands.

According to my invention I provide means for controlling the speed of the rolls of the penultimate stand and maintaining a relationship between the speeds of the last two stands such that the strip between the stands is maintained between zero tension and a slight compression. This permits close coupling of the last two stands.

It is therefore an object of my invention to provide a method of rolling strip in which the final stand is driven at a constant speed and the speed of the penultimate stand is varied to prevent the strip from necking down between the stands.

Another object is to provide an apparatus suitable for carrying out my method.

Still another object is to provide apparatus for rolling strip in which the last stand is driven at a constant speed and in which the distance between the last two stands is reduced from that normally used, thus decreasing the cost of the mill.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIG. 1 is a schematic side elevation of the last two roughing mill stands of a continuous hot strip mill utilizing my invention and showing the strip in a horizontal or fiat position between the stands;

FIG. 2 is a view, similar to FIG. 1, but showing the strip in a looped position between the stands; and

FIG. 3 is a schematic plan view of the mill of FIGS. 1 and 2 showing schematically the drive and controls of my, invention.

gReferring more particularly to the drawings, reference numeral 2 indicates the penultimate stand of a hot strip mill. Work rolls 4 of the stand are driven by a variable speed DC. motor 6. Power for the motor 6 is obtained from an A.C. power line 8 through a variable voltage converter 10 which may be a conventional motor generator set or a static converter which provides a variable DC. power supply. A conventional load detector 12 is placed in the line 8 to indicate whether or not the motor Patented Jan. 12, 1971 6 is receiving power. A roller table 14 is provided on the exit side of stand 2 so as to support a steel strip S and guide it to work rolls 16 of last roll stand 18. The rolls 16 are driven at a constant speed by means of a synchronous motor 20 which receives power from A.C. power line 22. A load detector 24 similar to load detector 12 is provided in the circuit to the motor 20'.

Light sources 26 are provided at spaced intervals between the rolls 4 and -16 at one side of and above the roller table :14. The light sources 26 which are shown as three in number must be located above the roller conveyor 14 a distance greater than the spacing between work rolls 4 so as to be out of line of the strip S when it is supported on table 14. In line with each of the light sources 26 on the opposite side of table 14 is a photocell 28. The light sources 26 and photocells 28 are preferably adjustably mounted for a purpose which will appear later. The combined output of photocells 28 is connected to a controller and signal accumulator 30 which is connected to control the converter 10. Signals from the load detectors 12 and 24 are connected to the accumulator 30. The accumulator 30 may take various forms, but is preferably a computer which takes the signals from the height detector when a strip is in both stands and operates the controller to vary the output of voltage converter 10, all in a way well understood by one skilled in the art.

The operation of my device is as follows:

The peripheral speed of rolls 4 is adjusted in a conventional manner so as to have a predetermined relationship with the peripheral speed of rolls 16. The speed of rolls 4 is necessarily less than that of rolls 16 since the strip thickness is being reduced and the strip lengthened. When the strip S enters the pass between rolls 4 and is reduced, a signal is generated in load detector 12 and transmitted to accumulator 30. The strip S reduced in thickness passes over roller table 14 into the pass between rolls 16 where it is further reduced in thickness. At this time a signal is generated in load detector 24 and is transmitted to accumulator 30. With the strip S in both stands, the ac cumulator 30 can then function responsive to the signals from photocells 28 to vary the output of the variable voltage converter =10. If the strip lies flat on the roller table 26-, as shown in FIG. 1, the light from light sources 24 is not interrupted and the signal from photocells 28 to the accumulator 30 is such as to cause the converter 10 to increase the speed of motor 6 and hence the speed of rolls 4. This will cause the strip S to tend to rise above the roller table 14. When the strip reaches the raised position shown in FIG. 2 the light from the middle light source 26 will be interrupted and the signal from photocells 28 to the accumulator 30 will be such as to cause the converter 10 to decrease the speed of the motor 6 and hence the speed of rolls 4. This will cause the strip S to return to a flat position on the roller table 14. This sequence of operation continues so as to keep the section of the strip S between the rolls 4 and 16 between zero tension and slight compression until the trailing end of strip passes through rolls 4 at which time the load de tector 12 signals that the strip is out of the rolls 4. This deactivates the accumulator 30. Adjustment of the elevation of light sources 26 and photocells 28 are made either to vary the height to which the strip S may move and/or to accommodate various thicknesses of strip between the rolls 4 and 16. It is preferred to have a plurality of height detectors as shown since the shape of the strip loop between rolls 4 and 16 may vary. It should also be understoodthat other types of height detectors, such as contact rolls or sound waves may be used in place of the photocells and lights.

While it is preferred to use the apparatus shown for carrying out my method it will be apparent that the method could be practiced by visual observance of the position of the strip S between the rolls 4 and 16 and manual adjustment of the converter 10 to maintain the strip between zero tension and slight compression.

While several embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made.

I claim:

1. Apparatus for rolling strip between a final pair of reducing rolls and a penultimate pair of reducing rolls which comprises means for driving said final rolls at a constant speed, means for driving said penultimate rolls at a variable speed less than said constant speed, detector means for determining when the strip passing between the penultimate and final reducing rolls is in a relatively straight path and when it rises a preset distance above said straight path, and means operable by said last named means for increasing the speed of the penultimate rolls when the strip is in a straight path and decreasing the speed of the penultimate rolls when the strip is in a raised position.

2. Apparatus according to claim 11 in which means for driving said final rolls at a constant speed includes a constant speed motor energized from a power line, and the means for driving said penultimate rolls at a variable speed includes a variable speed DC. motor energized from an AC. power line through a variable voltage converter.

3. Apparatus according to claim 2 in which the means operable by said last named means for increasing the speed of the penultimate rolls when the strip is in a straight path and to decrease the speed of the penultimate rolls when the strip is in a raised position includes a controller and signal indicator, and means connecting said controller and signal indicator to said variable voltage converter.

4. Apparatus according to claim 3 including a load detector in each of said power lines for indicating when a strip is between the respective pairs of rolls, and means connecting the outputs of said load detectors to said controller and signal indicator to prevent signals from said strip positioning means from operating said voltage converter except when strip is in both of said pairs of rolls.

15. Apparatus according to claim 4 including a roller table between said penultimate pair of reducing rolls and said final pair of reducing rolls at an elevation to receive said strip when in a straight path; and in which said detector means includes a plurality of spaced apart light sources located at one side of and above said roller table a distance greater than the spacing between the penultimate reducing rolls, and a photocell aligned with each of said light sources on the other side of the roller table. 6. A method of rolling strip between a final pair of reducing rolls and a penultimate pair of reducing rolls which comprises driving said final rolls at a constant speed, driving said penultimate rolls at a variable speed less than said constant speed, increasing the speed of said penultimate rolls when the strip between the penultimate and final rolls is in a substantially straight pass, and decreasing the speed of said penultimate rolls when the strip between the penultimate and final rolls rises to a predetermined distance above said substantially straight pass.

References Cited UNITED STATES PATENTS MILTON S. MEHR, Primary Examiner US. Cl. X.R. 72-234, 366 

